An X-ray generator is a valuable tool used in the medical and industrial field to perform non-invasive examinations. To generate X-rays, an X-ray tube and a high voltage power supply are required for operation. The X-ray tube is a vacuum tube which is usually a bipolar device with a cathode and filament at one end of the tube and an anode coated with tungsten at the other end of the tube facing the cathode. To produce X-rays, high voltage power supplies of positive and negative polarity are connected to the X-ray tube's anode and cathode respectively to create an extremely high voltage differential between the anode and the cathode. As current is passed through the filament at the cathode, the filament heats up and sputters off electrons at the cathode. The electrons are then drawn across the tube towards the positively charged anode at great speed and acceleration. When these accelerated electrons bombard the anode surface, energy is released in the form of heat and high-energy photons. These high-energy photons are commonly known as X-ray beams and have been used to perform noninvasive examinations in the medical and industrial fields because of their ability to pass though objects.
All X-ray generators require an extremely high voltage power supply to power the X-ray tube. Commonly, a voltage multiplier and a high frequency transformer are used to create this high voltage for advantage of size.
A popular voltage multiplier configuration commonly used in X-ray systems is known as the Crockroft-Walton configuration. In the Crockroft-Walton circuit, a basic block consisting of two diodes and two capacitors are used to make a voltage multiplier stage. Several stages are stacked together to step up the voltage to significant levels. The output voltage of a multistage voltage multiplier is nominally twice the input voltage times the number of stages. The packaging scheme requires particular attention because the extremely high voltages developed in the voltage multipliers can cause the high voltage to arc over between components and to other structures in close proximity.
The simplest way to stack the multiple stages of a voltage multiplier is to stack the multiplier stages in a straight line. The straight-line multiplier though simple to construct is often not optimal in size. The size of such a straight-line multiplier constrains practical location for the anode and cathode voltage multipliers in an X-ray generator. In a very compact x-ray generator, the preferred option is to place the voltage multipliers parallel to the X-ray tube but this can create other problems as well. When an X-ray tube is operating, X-ray radiation is emitted from the X-ray tube in all directions. This X-ray radiation can degrade non-radiation hardened components in the voltage multiplier. These susceptible components require X-ray shielding to protect them from the harmful radiation to prevent accelerated degradation. This X-ray shield must be placed between the X-ray tube and the multiplier components if the multiplier is placed parallel to the X-ray tube.
A secondary problem created by placing the multiplier components parallel to the X-ray tube concerns insulation between the X-ray tube, multipliers and the X-ray shield causing a complex interaction of the electric fields. When the shield is not used, the electric field created by the high voltage multipliers would interfere with the electric field homogeneity around the X-ray tube when the multiplier components are placed parallel to the X-ray tube. The shield, if used, also restricts efficient heat transfer around the X-ray tube due to high packing density of heat generating components. The use of an X-ray shield can be avoided by using radiation hardened electronic components but the cost of the X-ray generator system would be impacted. The availability of potential components would also be impacted as the selection of radiation-hardened components is limited. The X-ray shield, which is usually made from lead, adds to the size of the design and is inconsistent with the compact nature of the system.
For the reasons stated above, and for the reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a low cost, compact and lightweight low power X-ray generator where the voltage multipliers are reduced in size and use of lead is minimized. There is also a need for a compact low power X-ray generator where the intelligent design of the multipliers facilitate homogeneous distribution of electric field and efficient heat transfer around the X-ray tube.